HRP-filled microelectrodes have been used to investigate delta-type ganglion cell responses and morphology in the cat retina. Distinct both morphologically and physiologically from beta/x- and alpha/y- types, the photic response contains both sustained on-excitatory and transient on-inhibitory components, overlapping in both space and time. Electron-microscopy reveals synaptic input in s3 from type cb5, depolarizing cone-bipolar cells, and from three amacrine cell types, recognizable by distinctive electron-microscopic profiles. The cell appears to be an unorthodox ON-center unit. In the outer plexiform layer of the cat retina background stimuli enhance the responses of horizontal cells to small red flickering spots. This effect is more pronounced at higher flicker- frequencies, and is mediated through background-induced stimulation of peripheral rods, as demonstrated by spectral sensitivity studies. The effect declines with test spot width, with a mean space contact of 188+21um, comparable to the syncytial space constants of horizontal cells. These cells appear to provide a conduit for background-induced rod-signals to decrement into the test spot region, and facilitate synaptic transmission between cones and second-order retinal interneurons. Voltage- and transmitter-modulated currents induce and modify the photic responses of retinal ganglion cells. To render retinal ganglion cells accessible to electrophysiologic investigation of membrane currents by the patch clamp method, these neurons have been isolated from rat retinas and cultured. They first appear as large round cells, losing their original dendrites. New neurites grow do novo within several days. The conditions which promote survival and growth of neurites have been investigated.